This is Barry Belosis, one of the musculoskeletal radiology fellows at Stanford University. Fifteen-year-old female soccer and track athlete present with right anterior thigh pain, concern for chronic distal myotendinous junction, rectus femoris tear. Patient in this case presents with this right femur radiograph. Radiograph could be obtained to exclude any bony abnormalities. However, in cases of muscle strain, radiographs are typically normal. The patient in this case presented with this MRI without contrast. Here on our Axial T2 Fatsat imaging, we can see some edema right here and also here, predominantly involving the inner muscle belly of the rectus femoris. These findings are consistent with likely subacute low-grade strain of the rectus femoris. A quick review of our anatomy here depicts a normal direct head right here, which will attach to its origin at the anterior inferior iliac spine. Just posterior to this, we can see the indirect head right here, which will attach at the superior acetabular ridge and posterolateral aspect of the hip joint capsule. The two heads right here will form a conjoined tendon about 2 cm distal to their origin, as we can see here. However, rectus femoris muscle is unique in that it forms a muscle within a muscle configuration. The inner portion right here, or the inner muscle belly, forms a bipennate configuration around the central aponeurosis. The inner muscle belly arises from the indirect head, whereas the superficial muscle belly, which envelops this inner muscle belly, comes from the direct head. This makes muscle strain grading for rectus femoris unique. For example, in this patient with football player, grade 1 strain is demonstrated by T2 high signal or bright signal with a feathery appearance at the myotendinous junction, such as what we can see here. This low grade or grade 1 strain predominantly involves the inner muscle belly around the central aponeurosis. As we can also see here in our axial T2 FATSAT imaging, we can see this feathery appearance, but there is no discontinuity of the fibers. Our sagittal T2 steer demonstrates this craniocaudal extension, such as here. This is on a different football player, demonstrating a grade 2 strain approximately. In this case, we can see that there is significant edema and feathery appearance of the rectus femoris, but in this case, we can see that it involves the inner muscle belly right here, but it also involves the superficial muscle belly arising from the direct head in the anterior lateral aspect of this muscle. These findings are consistent with grade 2 strain, which is a grade 1 features with fiber disruption, which we can see in this area here. This is on a different patient, a 27-year-old wide receiver. Grade 3 strain is characterized by complete disruption and retraction of the fibers with local hematoma. In here, we can see an axial T2 FATSAT imaging demonstrating this hematoma, and on our coronal T2 FATSAT imaging, we can see this torn fibers, which is retracted distally. In the proximal aspect, we can see the hematoma, and there is this surrounding edema about the rectus femoris. Additional rectus femoris injury is what we call degloving injury, where the inner muscle belly is torn from the superficial muscle belly and retracted.

2nd Edition, CASE 29

2nd Edition

Knee

rectus femoris strain

muscle edema

MRI findings

strain grading

degloving injury